I ran across this googling for info. Seems like a good way to get a wideband meter for cheap -- about $10-15 in parts for the gauge & a junkyard O2 sense would probably make it functional for $30-40 total investment...
http://www.scirocco.org/tech/misc/afgauge/af.html
I won't have time to build this for a while; if any of you do be sure to post how well it works.